Numerical simulation of boron injection in a BWR

The present study constitutes a first step to understand the process of boron injection, transport and mixing in a BWR. It consists of transient CFD simulations of boron injection in a model of the downcomer of Forsmark’s Unit 3 containing about 6 million elements. The two cases studied are unintentional start of boron injection under normal operation and loss of offsite power with partial ATWS leaving 10% of the core power uncontrolled. The flow conditions of the second case are defined by means of an analysis with RELAP5, assuming boron injection start directly after the first ECCS injection. Recent publications show that meaningful conservative results may be obtained for boron or thermal mixing in PWRs with grids as coarse as that utilized here, provided that higher order discretization schemes are used to minimize numerical diffusion. The obtained results indicate an apparently strong influence of the scenario in the behavior of the injection process. The normal operation simulation shows that virtually all boron solution flows down to the Main Recirculation Pump inlet located directly below the boron inlet nozzle. The loss of offsite power simulation shows initially a spread of the boron solution over the entire sectional area of the lower part of the downcomer filled with colder water. This remaining effect of the ECCS injection lasts until all this water has left the downcomer. Above this region, the boron injection jet develops in a vertical streak, eventually resembling the injection of the normal operation scenario. Due to the initial spread, this boron injection will probably cause larger temporal and spatial concentration variations in the core. In both cases, these variations may cause reactivity transients and fuel damage due to local power escalation. To settle this issue, an analysis using an extended model containing the downcomer, the MRPs and the Lower Plenum will be carried out. Also, the simulation time will be extended to a scale of several minutes.     

Enhanced multiple-point beam-to-beam frictionless contact finite element

In this paper a new contact finite element for beams with circular cross-sections is presented. The element is an enhancement of the previously formulated point-wise beam-to-beam contact finite elements to be used in cases when beams get in contact at very acute angles. In such situation, if beam deformations in the vicinity of the contact zone are taken into account, the contact is not point-wise but it extends to a certain area. To cover such a case in a more realistic way, two additional pairs of contact points are introduced to accompany the original single pair of contact points. The central pair is determined using the orthogonality conditions for the beam axes and the positions of two extra points are defined on one beam axis by a shift of the local co-ordinate. This shift depends on beams geometry and the current angle between tangent vectors at the central contact point. The appropriate kinematic variables for normal contact together with their finite element approximation are derived. Basing on the weak form for normal contact and its linearisation, the tangent stiffness matrix and the residual vector are derived. The new element is tested using author’s computer programs and comparisons with the point-wise contact elements are made.     

Impedance studies of copper electro-reduction on a disc-shaped ultramicroelectrode in industrial electrolytes

The electrodeposition of copper from industrial sulphate electrolytes has been studied using electrochemical impedance spectroscopy on the gold disc ultramicroelectrode. The influence of dc potential E _dc , temperature, cupric ions and animal glue concentration on electrochemical impedances has been investigated. The mechanism of the copper electro-reduction process in industrial electrolytes has been proposed and experimental impedance data have been analyzed by proper equivalent circuits. According to our knowledge the faradaic and non-faradaic impedance parameters of the process on ultramicroelectrode’s have been estimated for the first time in complex matrix copper industrial electrolytes. The role of animal glue in copper industrial electrolytes has been discussed in the present paper.     

The cyclic voltammetry simulation of a competition between stepwise and concerted dissociative electron transfer,the modeling of alpha apparent variability,the relationship between apparent and elementary kinetic parameters

A comparison of elementary (input) and apparent (output) values of the transfer coefficient was carried out for simulated kinetic cyclic voltammetry spectrum from stepwise to concerted mechanism. The resulting patterns of alphaapp versus Ep plots do not provide sufficient information to discriminate between the two mechanisms. It has been demonstrated that non-linear alphaapp patterns are characteristic for the pure stepwise mechanism obeying the Butler-Volmer kinetics. The change in alphaapp is not a sufficient condition for the transition from stepwise to concerted mechanism. This paper contains visualizations of the relationship between the apparent and elementary transfer coefficient. The difference between the potential variabilities of alphaapp and alphaelem (a frequent source of confusion) is also discussed.     

Searching for nonlinear feedback shift registers with parallel computing

Nonlinear feedback shift registers (NLFSRs) are used to construct pseudorandom generators for stream ciphers. Their theory is not so complete as that of linear feedback shift registers (LFSRs). In general, it is not known how to construct all NLFSRs with maximum period. The direct method is to search for such registers with suitable properties. Advanced technology of parallel computing has been applied both in software and hardware to search for maximum period NLFSRs having a fairly simple algebraic normal form.     

Wetting of Sn-Zn-<Emphasis Type=Italic>x</Emphasis>In (<Emphasis Type=Italic>x</Emphasis> = 0.5, 1.0, 1.5 wt%) Alloys on Cu and Ni Substrates

Wetting angles of Sn-8.8Zn and Sn-8.8Zn-xIn alloys (x = 0.5, 1.0, 1.5 wt%) were studied with the sessile drop method. Wetting tests were carried out for 900 s in the presence of ORM0 flux at 493, 523, and 573 K on copper and at 523 K on nickel substrates, respectively. It was found that the addition of In to Sn-8.8Zn alloy improves its wetting on both substrates by reducing the value of apparent wetting angle. Also, with increasing temperature a decrease of wetting angle on copper is observed in the case of 0 and 1.5 wt% of In alloys. Solidified solder-substrate couples were cross-sectioned and examined with scanning electron microscopy coupled with electron dispersive X-ray analysis. Interlayers were found at the interface of solders with copper and nickel, and their compositions are close to Cu₅Zn₈ and Ni₅Zn₂₁ intermetallics, respectively. However, in the case of Sn-8.8Zn-1.5/Ni couple small scallops are observed instead of continuous interlayer.     

Particle swarm intelligence tunning of fuzzy geometric protoforms for price patterns recognition and stock trading

A novel approach for detecting patterns in price time series is shown. The proposed system for identifying consolidation phases is based on fuzzy geometric protoforms and classification trees. Promising results of the empirical studies prove that the suggested fuzzy geometric protoforms are very useful for identifying patterns in graphical visualizations of data. Moreover, the architecture of the system enables successful incorporation of genetic optimization what enables capturing various data sets structure and unstable conditions on financial markets.     

Aggregation of polylactide with carboxyl groups at one chain end in the presence of metal cations

Polylactides with one or more carboxyl groups at one chain end were synthesized by cationic polymerization according to activated monomer mechanism and by application of “thiol-yne” click chemistry for subsequent functionalization. End groups of such obtained polylactides were converted into ionic groups by neutralization of polymer solutions with metal oxides, mainly calcium oxide, and the aggregation of individual stereoisomers as well as that of the mixture of poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) was investigated. The extent and progress of the aggregation was followed by viscosity measurements, and aggregated polymers in the solid state were examined by SEM and DSC. Solution viscosity increase was observed upon the aggregation of individual PLA stereoisomers, whereas PLA stereocomplex precipitation occurred in the case of the aggregation of PLLA/PDLA/metal oxide mixture.     

Lipid composition and cell surface hydrophobicity of Candida albicans influence the efficacy of fluconazole–gentamicin treatment

Adherence of the fungus, Candida albicans, to biotic (e.g. human tissues) and abiotic (e.g. catheters) surfaces can lead to emergence of opportunistic infections in humans. The process of adhesion and further biofilm development depends, in part, on cell surface hydrophobicity (CSH). In this study, we compared the resistance of C. albicans strains with different CSH to the most commonly prescribed antifungal drug, fluconazole, and the newly described synergistic combination, fluconazole and gentamicin. The hydrophobic strain was more resistant to fluconazole due to, among others, overexpression of the ERG11 gene encoding the fluconazole target protein (CYP51A1, Erg11p), which leads to overproduction of ergosterol in this strain. Additionally, the hydrophobic strain displayed high efflux activity of the multidrug resistance Cdr1 pump due to high expression of the CDR1 gene. On the other hand, the hydrophobic C. albicans strain was more susceptible to fluconazole–gentamicin combination because of its different effect on lipid content in the two strains. The combination resulted in ergosterol depletion with subsequent Cdr1p mislocalization and loss of activity in the hydrophobic strain. We propose that C. albicans strains with different CSH may possess altered lipid metabolism and consequently may differ in their response to treatment.     

N-nitrosodimethylamine (NDMA) as a product of potassium permanganate reaction with aqueous solutions of dimethylamine (DMA)

The reactivity of permanganate with dimethylamine, as possible path of NDMA formation, has been investigated.The results have shown that potassium permanganate reaction with aqueous solutions of dimethylamine (DMA) leads to the formation of N-nitrosodimethylamine (NDMA). The contact time, the molar ratio of permanganate and DMA, pH and presence of nitrite are the key factors influencing the efficiency of NDMA formation. Significant conversion rates of DMA to NDMA were observed only for the high doses of permanganate, which were many times higher than those typically used in water treatment. This reaction however is of importance for water treatment technology, since it shows the possibility of NDMA formation as a result of oxidation of DMA.It is likely that nitrosation is the main path of the reaction. An important role of MnO₂ suspension, formed as a result of permanganate reduction in NDMA formation is emphasized. Significant influence of MnO₂ suspension on NDMA formation should draw our attention to the potential impact of MnO₂ activated filtration beds on NDMA formation.